AAVERAGE()

  Short:
  ------
  AAVERAGE() Determines average of an array with condition

  Returns:
  --------
  <nAverage> => Average of the array

  Syntax:
  -------
  AAVERAGE(aTarget,[bCondition])

  Description:
  ------------
  <aTarget> is the target array. Normally an array of numeric values.

  [bCondition] is an optional codeblock used to select
  a subset of the array. This could be used to filter out 0's or
  non-numeric elements. The block must accept an array element as
  a parameter, and return true or false <expL> to determine if
  this element is part of the desired subset.

  Examples:
  ---------
   v := AAVERAGE(aSales)
   v := AAVERAGE(aSales,{|e|valtype(e)=="N".and.e<>0})

  Source:
  -------
  S_ASTATS.PRG